In agriculture, devices are known in the shape of either smooth or toothed disc. By rotating due to land contact, such discs are able to dig groove on the land, to execute operations like ploughing, seeding, fertilizer spreading and other similar operations.
Usually, such discs are assembled side by side to correspondent shafts, which embossed protrude from the frame of an agricultural machine. Each disc is rotatable assembled, by means of a hub-bearing assembly, which comprises one or two radially inner rings, stationary, the inner rings steadily fixed to a central shaft, which embossed protrudes from an arm of the frame of an agricultural machine. The hub-bearing assembly also comprises a radially outer ring and a double row of balls, which is interposed between the outer ring and the inner rings. The inner rings, and consequently the bearing, are axially locked against the shoulder of the shaft, due to the tightening of a sleeve or a nut, which is screwed at a free end of the shaft. The outer ring can be contained in a housing, which is in one piece with an external radial flange, for assembling the disc. The housing is covered by a closing cap, which can be press-fit into the housing or screwed on it.
The housing, surrounding the outer ring, is normally made of plastic material and can be co-molded on the outer ring, according to a known technology. After co-molding, the cooling of the plastic material causes a dimensional reduction of the housing and, consequently, a radial interference between the radially inner surface of the housing and the radially external surface of the bearing outer ring.
Such hub-bearing assemblies are well known and have been disclosed in several documents, for example U.S. Pat. No. 3,083,972 A and US 2007/074879 A1.
Unfortunately, the radial interference between housing and outer ring is not enough, to let the assembly be suitable for all prescribed applications. At the same time, solutions aimed to improve the grip between metal and plastic (for example, creating a plurality of grooves all along the ring external surface, inside which the liquid plastic of the housing to be co-molded can flow) are part of non-conventional hub-bearing assemblies, which are more expensive.
Example of retention means to improve the grip between housing and ring are shown in GB 1520341 A, U.S. Pat. No. 6,106,156 A, DE 10347361 A, DE 19713333 A1, DE 19860345 A1, US 2005/105840 A1.